1. Field of the Invention
The present invention relates to marine craft. More particularly, the present invention relates to the rudders of marine craft. Still more particularly, the present invention relates to flap rudders.
2. Description of the Prior Art
A rudder in the form of a pivotable plate or a displacement body is disposed at the stern of a ship. When the rudder is actuated, it is pivoted by a controlled angle of deflection. That movement develops a hydrodynamic transverse force which acts on the rudder and correspondingly on the stern of the ship. This force produces the turning torque required to steer the ship. This hydrodynamic transverse force produces a torque on the rudder with respect to the rudder stock which is to be supplied by the steering gear.
There are single member rudders, flap rudders and geared flap rudders. The current basic arrangement for a geared flap rudder includes a rudder member with an associated fixed gear that engages with a flap member having an associated movable gear. The rudder member is oriented forward of the flap member when viewing the vessel bow to stern. The forward gear of the rudder member is joined to the hull and the aft gear of the flap member is joined to the flap member. As the rudder stock is turned, the flap angle is double the rudder angle. There are no sliding parts, no energy absorber and no bearings other than on the flap member to the rudder member. In another design, the rudder member includes a positively controlled fin that is deflected in opposition to the main rudder deflection without the aid of powered steering gear in order to establish torque equilibrium with respect to the rudder stock.
A limitation of the existing geared flap rudder design is experienced when the rudder member or the flap member is bent, such as may occur when either contacts large debris. If the bend is significant enough, it is not possible to move either or both of the rudder member and the flap member as desired to change their respective positions. That circumstance will compromise ship maneuverability. Another limitation of the existing geared flap rudder design occurs when debris, such as a log for example, wedges into the gearing, rendering it difficult or impossible to change the position of the gear. That too, will compromise the ability to maneuver the ship.
What is needed is a geared flap rudder that is configured to minimize the operation of the rudder when either or both of the rudder and the flap are impacted and bent. What is also needed is a geared flap rudder that is configured to avoid gear lockup resulting from debris getting into the gears that exist on the flap and the rudder. The geared flap rudder should remain functional for normal operations whether or not the flap, the rudder or the gears are compromised.